The present invention relates generally to irrigation control system and, more particularly, to sequential irrigation control systems in which water valves are actuated one at a time and in a predefined sequence.
In a typical, relatively small irrigatin system, many sprinklers are supplied from a single water supply line, and only a single sprinkler, or group of sprinklers, is actuated at a time. In a normal watering sequence, the sprinkler or sprinklers at a first valve station are turned on for a predetermined time, then the sprinkler or sprinklers at the next valve station are turned on for a different predetermined time, and so on, until an entire watering cycle has been completed. There are, of course, many control systems, some of which are quite complex, for initiating and timing such a watering sequence. Such systems usually require a relatively expensive central timing mechanism, which communicates with a plurality of valve stations, either by many pairs of conductors or by means of encoded control signals transmitted over two or three conductors. In any event, such systems are quite costly, and are therefore unsuited for such applications as residential irrigation.
One alternative to a complex central timing device is exemplified by U.S. Pat. No. 3,989,066 to Sturman et al., wherein a separate timing unit is employed at each valve station, and the valve stations are connected by a pair of lines in a series string. The first valve in the string is actuated for its preselected time, after which it automatically switches power to the next valve in turn, which then remains actuated for its preselected time, and so on. In another system of the prior art, described in U.S. Pat. 3,723,827 to Griswold et al., a central timer is used, and power is supplied over a pair of lines to a series string of valve control units, the power being switched from one unit to the next in response to short interruptions in the operating voltage supplied at the central site. Another system, described in U.S. Pat. No. 3,113,724 to De Bough is similar to the one described in the aforementioned Sturman et al patent, except that individual timers at the valve stations are not employed, but rather the conditions of water sensors determine the termination of watering at the stations.
Accordingly, there is still a need for a low-cost sequential irrigation controller system which is readily adaptable for control by a central timing and control unit or by manual means at the central site. The present invention is directed to this end.